In the use of water soluble polymer flocculants, one problem is how to dissolve the polymer into water so that it can be utilized for its intended purpose. Early water soluble polymers were provided as dilute aqueous solutions. As the technology improved, and the molecular weights of the polymers were improved, it becomes increasingly difficult for manufacturers to ship these polymers in solution form because of the high viscosity of even one-half to one percent solutions of the polymers. Manufacturers accordingly started shipping the polymers in the form of comminuted solids which could be dissolved into water using various mechanical means. While solving shipment problems, some mechanical means degraded the polymers through shear, and, incomplete dissolution of water soluble polymers, the formation of swollen translucent particles, was common. This led to a waste of polymer, and in some cases, detrimental results such as in the case of so called “fish-eye” particles which caused defects in the manufacture of paper. In the early 1970's water-in-oil emulsions of water soluble polymers were introduced. Using the water-in-oil technology, high molecular weight polymers that rapidly dissolved could be produced, and this technology achieved great acceptance in the water soluble polymer industry. A disadvantage of the water-in-oil emulsion polymer technology however is that the emulsions contain substantial quantities of hydrocarbon liquid. The introduction of hydrocarbon liquids into the systems where these water soluble polymers are used is not always beneficial.
In the manufacture of paper, a papermaking furnish is formed into a paper sheet.
The papermaking furnish is an aqueous slurry of cellulosic fiber having a fiber content of less than 4% by weight (percent dry weight of solids in the furnish), and generally about 1.5% or less, and often below 1% ahead of the paper machine, while the finished sheet typically has less than 6% by weight water. Hence the dewatering and retention aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
Various chemical additives have been utilized in an attempt to increase the rate at which water drains from the formed sheet, and to increase the amount of fines and filler retained on the sheet. The use of high molecular weight water-soluble polymers is a significant improvement in the manufacture of paper. The high molecular weight polymers act as flocculants, forming large flocs which deposit on the sheet. They also aid in the dewatering of the sheet.
There is a continuing need to develop more efficient retention aids and processes for producing the same.
U.S. Pat. No. 5,605,970 discloses a method for the manufacture of a particular anionic water soluble polymer in dispersion form. This disclosure teaches that certain anionic polymers, incorporating hydrophobically modified monomers, can be prepared using dispersion polymer methods. The application specifically teaches the manufacture of acrylic acid-ethylhexylacrylate polymers. The ethylhexylacrylate monomer adds a hydrophobic character to the polymer, causing the polymer to become insoluble in certain brine solutions. While these polymers, and the methods for their manufacture are useful, the incorporation of a hydrophobic monomer into a water soluble polymer, where water solubility is desirable is not always advantageous in the final use of the polymer. Moreover, the useful stabilizer disclosed therein is described as having low levels of some hydrophobic monomer along with NaAMPS and/or sodium acrylate.
EP 0 183 466 discloses a process for the production of a water-soluble polymer dispersion in the presence of a dispersant, wherein the dispersant may be a poly(2-acrylamido-2-methyl propane sulfonic acid (AMPS)) or a copolymer having 30 or more mole percent of AMPS.
U.S. Pat. No. 5,837,776 discloses a composition and a method of making a dispersion in the presence of a stabilizer copolymer, wherein the stabilizer copolymer contains at least 20 mole percent acrylamidomethyl propane sulfonic acid. The dispersion polymers prepared as described in this patent are prepared at a pH of from 2 to 5.
U.S. Pat. No. 6,417,268 discloses a method for making hydrophobically associative polymers using a brine dispersion method. The method comprises forming a monomer solution containing a surfactant, a hydrophobic monomer, a hydrophilic monomer and water, mixing the monomer solution and a salt solution containing a multivalent salt, stabilizer and water, and charging the mixed solution with an initiator to cause polymerization. The stabilizer is crucial to the method since it affects the homogeneity of the dispersion. Preferred stabilizers are vegetable gums, polysaccharides and cellulose products.
WO 01/18064 discloses a high molecular weight water-soluble dispersion polymer and a method of preparing the same. The dispersion polymer comprises from about 5 to about 50% by weight of a water soluble polymer prepared by polymerizing under free radical forming conditions in an aqueous solution of a water-soluble salt in the presence of a stabilizer 0-30 mole percent of at least one anionic monomer, and 100-70 mole percent of at least one non-ionic monomer, wherein the stabilizer is an anionic water soluble polymer, and the water soluble salt comprises from 5 to 40% by weight based on the weight of the dispersion. The polymerization is carried out at a pH greater than 5.
WO 01/18063 discloses a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish an effective flocculating amount of a high molecular weight water-soluble dispersion polymer defined in the above WO publication.